1. Field of the Invention
The present invention relates to a sheet process apparatus for aligning sheets stacked on a sheet process tray.
2. Related Background Art
Up to now, in some image forming apparatuses such as a copying machine, a printer, a facsimile, and a multifunctional apparatus, a sheet process apparatus for performing a process such as a binding process with respect to sheets delivered from an image forming apparatus main body is provided in the image forming apparatus main body.
Some sheet process apparatuses stack delivered sheets on a process tray, align them, and then, perform a process such as a binding process with respect to the sheets (i.e., a sheet stack or sheet bundle). Further, some sheet process apparatuses wind a plurality of sheets around a buffer roller once, without directly feeding the delivered sheets to the process tray, so the sheets can be transported to the process tray together with a subsequent sheet.
Some sheet process apparatuses with such a configuration, for example, have a path 1160 for winding around a buffer roller 1151 capable of overlapping a plurality of sheets, as shown in FIG. 17. Sheets are wound around the buffer roller 1151 under the condition that a previous stack PA is processed in a process tray 1138.
Then, a plurality of sheets are wound around the buffer roller 1151, whereby a process time in a process tray 1138 with respect to the sheets delivered at a high speed and at a small sheet interval from the image forming apparatus main body can be ensured (see JP-A-H10-181988).
A plurality of sheets wound around the buffer roller 1151 as described above are transported to the process tray 1138 under the condition in which those sheets are overlapped. Then, the sheets are sandwiched between discharge rollers 1128 and stack discharge rollers 1130a, 1130b, and transported until sheet trailing ends come out of the discharge rollers 1128. Further, after this, the sheet bundle PA is returned to a trailing end regulating member side (not shown) of the process tray 1138 by the reverse rotation of the stack discharge rollers 1130a, 1130b shown in FIG. 18.
Herein, by separating the stack discharge roller 1130b from the stack discharge roller 1130a before the trailing end of the sheet bundle PA comes into contact with the trailing end regulating member, and pressing the trailing end of the sheet bundle PA against the trailing end regulating member by return means such as a paddle (not shown), the trailing end regulation of the sheet bundle PA is performed. After such trailing end regulation, the sheet bundle PA is aligned in a direction (hereinafter, referred to as a lateral direction) orthogonal to a sheet transport direction of the sheet bundle PA by an aligning plate (not shown).
In such a conventional sheet process apparatus, for example, when three overlapped sheets are transported to the process tray 1138, a middle sheet P2 may be displaced in the lateral direction for some reason, for example, as shown in FIGS. 19A and 19B. To be more specific, the middle sheet P2 may protrude in the lateral direction, compared with the upper and lower sheets P1 and P3.
In this case, when an aligning plate 1 is moved toward an aligning plate 2 so as to align the sheet bundle PA in the lateral direction, the aligning plate 1 presses a side end of the sheet bundle PA. At this time, in particular, when the aligning plate 1 presses an upstream side in the transport direction of the sheet bundle PA, the middle sheet P2 may be in a tilted state when the aligning plate 1 reaches a predetermined alignment completion position.
Herein, the trailing end regulation of the sheet bundle PA is performed again after such alignment in the lateral direction is performed. In such a state, the upper and lower sheets P1 and P3 generate resistance, with the result that the middle sheet P2 cannot move to the trailing end regulating member side even if the self weight or the return means is acted. Consequently, alignment displacement is caused as shown in FIG. 19C.
That is, in the case where the middle sheet P2 protrudes in the lateral direction, compared with the upper and lower sheets P1 and P3, the upper sheet P3 returns first, which generates resistance, with the result that the middle sheet P2 cannot return to cause an alignment defect. This phenomenon is conspicuous particularly in the case where a sheet P has a large size such as an A3size, because the pressing position of the aligning plate 1 falls on a trailing end side with respect to the center of gravity of the sheet P.
In the case of placing sheets on the process tray 1138 one by one, the sheet P1 can be returned to the direction of the trailing end regulating members 3 and 4 by the self weight or the return means, even if the sheet P1 tilts after the alignment as shown in FIGS. 20A, 20B and 20C.
In order to overcome the above problem, it is possible that the aligning plate 1 is set to be longer (or larger) in the sheet transport direction. However, for example, in an apparatus in which sheets are stacked across the process tray 1138 and a stack tray 1137 shown in FIG. 17 so that the apparatus is miniaturized, the process tray 1138 is made to be long, which enlarges the apparatus. Further, it is also possible that aligning means replacing the aligning plate is placed separately on the stack tray 1137. In this case, however, the apparatus is made to be complicated.